We are investigating the chemical composition and function of filamentous proteins in the vertebrate nervous system. We have recently found that a tropomyosin-like molecule is present in the brain and in growing nerve cells. It is an alpha-helix; forms periodic paracrystals; and can bind to muscle actin, replacing muscle tropomyosin in a Ca ions activated ATPase system. We are presently comparing the structure of this molecule with various muscle and non-muscle tropomyosins. We are also attempting to localize this molecule in the growing neuron, using fluorescent antibody methods. We have developed a sensitive method for determining the peptide maps of proteins removed from stained SDS-acrylamide gels, and are using this technique to attempt to demonstrate the presence of tropomyosin, as well as actin, myosin, and tubulim, in rat synaptosome preparations. We hope to demonstrate the role of these proteins in synaptic neurotransmitter release. We are also investigating whether the synthesis of actin and tubulin in 3T3 fibroblasts depends on whether the cells are dividing or are stationary. Our preliminary evidence suggests that these proteins are not synthesized to as great an extent in confluent cells.